http://techstartu.ps is starting to gain some traction and is significantly more focused on startups than HN is.
The articles are ok though (but quite a few got posted here as well).
But the discussion is just about non-existent. I've gotten a bit wary of HN split-offs, they tend to be very short-lived.
I don't know what the main reason for that is, possibly it is simply that HN is 'good enough' and that a splinter of it does not carry enough volume for long term sustainability.
The comments will come with time; right now there aren't many contributors, but the site has been around long enough and been updated frequently enough that I believe it will stick around. HN was kind of slow moving when it started, too (although not that slow, to be honest).